Human hair consists of a root embedded in the skin and a shaft projecting from the skin surface. The root ends in the hair bulb which is a soft, whitish enlargement. The bulb is lodged in an elongated pit in the skin, called the follicle. If the hair is long, the follicle extends into the subcutaneous fatty tissue beneath the skin. At the base of each follicle is a conical swelling called the papilla. The papilla and follicle are supplied with nerves and blood vessels. Hair growth takes place at the junction of the follicle and the papilla. As the cells are pushed up the follicle, they harden and become the hair strand.
A small muscle is attached to each hair follicle. If the muscles are contracted, the hairs become more erect and the follicles are dragged upward, producing small bumps on the surface of the skin, called gooseflesh. Sebaceous (fat) glands attached to each hair release sebum which lubricates the hair. Excess sebum tend to make the hair look unsightly.
Hair growth is not a continuous process, but progresses for a variable period and then stops. The approximate 150,000 hairs of the scalp are able to grow for years without interruption. Baldness, or alopecia, occurs because of a natural tendency of the follicles of the scalp to become very small as humans age/Common baldness is hereditary and occurs more frequently in men than in women. Good grooming and hygiene are essential in providing healthy and good-looking hair and various aids and agents are available to help in achieving this status.
The basic cleaning agents in soaps and detergents are called surface-active agents, or surfactants When added to a liquid, they reduce its surface tension (the affinity that the surface molecules have for each other), thereby increasing the liquid's spreading and wetting properties. Part of the surface-active molecule must be hydrophilic, or "water-loving", and part must be hydrophobic, or water-repellent. Surface-active molecules concentrate at the interfaces, or areas of contact, between water and oil. One end of the molecule seeks the water; the other end seeks oil (or air, if the interface is between water and air). At water-oil interfaces, surface-active against emulsify oil--they mix it into the liquid the wa fat is mixed in milk; at water-air interfaces, they trap air molecules to produce foam.
There have been many attempts to create a solution which when applied to the hair, creates a thicker more abundant look even though no new hair growth is created. Moreover, there have been many attempts to create a mixture which when applied to the hair, changes or corrects the chemistry of the hair.
See, for example, U.S. Pat. No. 4,136,188, "Treating Hair with Cosmetic Formulations containing Polypeptides", which attempts to correct the pH balance of the chemistry of human hair after it has been altered by another cosmetic treatment.
Many other formulations for improving the condition of human hair contain various surfactants. See, for example, U.S. Pat. Nos. 4,964,874 for "Hair Treatment Product; Cationic Surfactant, Fatty, Alcohol and Dye Mixture"; compare, 4,855,130 for "Hair Treating Compositions and Processes for Improving the Condition of Hair; Synergistic Mixture of Glycerin and Organic Acid".
In general, hair conditioning treatments may also contain in addition to surfactants and synthetic polymers, thickeners, antioxidants, organic acids, perfume oils and other ingredients. See, for example, U.S. Pat. Nos. 4,752,467 for "Hair Treatment Agent and Method for Improving the Condition of Hair; Mixture of Trimethyl Ammonia Acetate Betaine and Organic Acid" and 4,726,945 for "Hair Rinse Conditioner; Mixture of Quaternary Ammonium Compound, Alkylamidodiakylamine, Propylene Glycol, Mineral Oil, Fatty Alcohol and Siloxane".